It's too bad Nadal just wasted 6 months of his prime and 2 Slam opportunities. These months don't ever come back. The window is small for physical players like Nadal to really accumulate the titles, especially with the intense level of growing competition. After beating Djokovic 3 times on clay, even with the Wimbledon loss, he should've been there at the USO and AO to try to crack Djokovic even more. Instead he had a 6 month holiday while Djokovic won a Masters, a WTF and a Slam and is now even more confident and playing better than before. On top of that, Murray's just made massive inroads on the top players, having won the Gold and the USO.
Nadal should've been there trying to stop both of these guys from gaining confidence and improving their games.
Now he has to not only work double hard to improve his own form but work even harder than that to try to gain any kind of edge on the younger guys who've elevated their games during his absence.